Mercury 90 Fourstroke not charging all the time.

[BigDfromTN]

I have a 2005 Mercury 90hp fourstroke carbed engine. Had it out this weekend and checked charging gauge and it showed 12V. It normally reads 14V and was the day before. Later I fired up and headed out it was reading 12V, then went to 13V, and moved up to the 14V like normal.

Is this a common thing? ( I have not seen it do this before)
Is there something I need to check or that causes this on a regular basis?

Your thoughts and info are appreciated.

Don

 

[alldodge]

Not an outboard guy but sounds like it's working. The standard Merc alt will not start putting out full charge until rpms come up. Here is the test and output curve




Here is the manual http://boatinfo.no/lib/mercury/manuals/75-90.html#/122

 

[bruceb58]

Your alternator should be able to provide 20A at 1000RPM if its the same alternator that is on my engine. Been awhile since I have run my engine but I never have a voltage output of just 12V even at idle or just above.

 

[BigDfromTN]

Not an outboard guy but sounds like it's working. The standard Merc alt will not start putting out full charge until rpms come up. Here is the test and output curve




Here is the manual http://boatinfo.no/lib/mercury/manuals/75-90.html#/122

Thanks for the reply and posted info.

I did rev the engine in neutral and it still remained at 12V. Normally even at Idle it shows more than 12 V. as mentioned by bruceb58.

After a little while it did start charging as if an intermittent bad connection. Anyone have an idea what I can check first? Was curious if this is a common problem that is caused by some weak link???

TIA, Don

 

[bruceb58]

Measure the voltage at the battery with a meter to confirm it isn't your gauge.

 

[BigDfromTN]

Measure the voltage at the battery with a meter to confirm it isn't your gauge.

Will do when I get back it back out this weekend. (Boat stays at our house at the river )

I also plan to check and clean connections on battery, Rectifier/Regulator and Stator. Engine never failed to crank or spin over real strong, so I doubt battery connections are the problem...

If anyone else has some info, chime right in!